U.S. Special Counsel Robert Mueller, tasked with pursuing collusion between Donald Trump’s presidential campaign and foreign interests, just planted his first stake in the heart of the Russian matter.

Prosecutors on Mueller’s team revealed Monday that a foreign policy adviser on Trump’s campaign, George Papadopoulos, pursued Russia’s help in the 2016 U.S. presidential campaign and sought to open communication lines to the Kremlin.

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Even more than the indictments of Paul Manafort and Rick Gates, the case — showing how Russians attempted to influence key Trump aides — lays out a blueprint for Mueller’s work as his prosecutors circle other campaign officials.

The case against Papadopoulos details repeated contact between Trump’s campaign team and agents working on behalf of Russian interests during the 2016 election campaign. Emails and testimony show that two high-level supervisors and other campaign officials involved in national security and foreign policy were aware of these communications.

The campaign also received information that the Russians had thousands of emails containing “dirt” on Democratic candidate Hillary Clinton months before hacked emails from the Democratic Party were made public.

Trump has repeatedly denied any efforts to collude with the Russians, and the guilty plea doesn’t say what the Trump campaign did with the information.

The White House press secretary, Sarah Huckabee Sanders, played down Papadopoulos’s role in the campaign on Monday. “This individual was a member of a volunteer advisory council that met one time over the course of a year,” she said, adding that “I’d hardly call that some sort of regular adviser or a senior member of the staff.”

A youthful adviser to the campaign, Papadopoulos interacted repeatedly with an international professor who promised compromising information from Russia about Clinton. He also met with a Russian woman he believed could broker a meeting between the campaign and Russian officials.

He then lied about the timing and content of those interactions to agents of the Federal Bureau of Investigation. Papadopoulos pleaded guilty to lying on Oct. 5 in a sealed document that was made public on Monday in Washington. Ominously for the White House, Papadopoulos is cooperating with the investigation.

Papadopoulos’s plea was unexpected on a day when Mueller’s charges were unsealed against Manafort, a former Trump campaign manager, and his longtime associate Gates, accusing them of money laundering, tax crimes and conspiracy related to their business dealings years before they joined Trump’s campaign.

Papadopoulos, 30, faces up to five years in prison and $250,000 in fines. His lawyers, Thomas Breen and Robert Stanley, said in a statement that it was in their clients’ best interest that they “refrain from commenting on George’s case.” Under the plea agreement with prosecutors, he’s likely to serve no more than six months and may avoid prison altogether.

Unlikely Pick

A 2009 DePaul University graduate who listed Model U.N. as a credential on his résumé, Papadopoulos was an unlikely pick to help lead the Republican candidate’s international policy team. A London resident, he had worked for Ben Carson’s presidential campaign.

He learned in early March 2016 that he would become a Trump foreign policy adviser, according to the government documents.

A few weeks later, when the Washington Post asked Trump to identify his foreign policy advisers, the Republican front-runner named Papadopoulos (an “excellent guy”) and four others including Carter Page, who has since been questioned by lawmakers and the FBI about whether he acted as a go-between with Russians.

Page has said that he’s answering investigators’ questions but that the Russia investigation is a witch hunt. He didn’t immediately return calls seeking comment.

Documents filed in the case against Papadopoulos expand significantly on what had been known about Papadopoulos’s overtures to the Russian government, including that others in the Trump campaign were at least aware of them.

“The Russian government has an open invitation by Putin for Mr. Trump to meet him when he is ready,” Papadopoulos wrote to a senior campaign adviser on April 25, 2016.

The documents referred to an unnamed campaign supervisor and a second campaign official who nixed Papadopoulos’s idea of setting up a meeting with President Vladimir Putin of Russia. The supervisor is quoted telling Papadopoulos in an email that “I would encourage you” and another Trump foreign policy adviser to “make the trip, if it’s feasible.”

The other campaign official forwarded a Papadopoulos email to another campaign official saying, “Let’s discuss. We need someone to communicate that DT is not doing these trips. It should be someone low-level in the campaign so as not to send any signal.”

Airport Arrest

Papadopoulos was arrested after arriving at Dulles International Airport on July 27, 2017, according to the court filing. The day before, FBI agents had executed a no-knock search warrant on Manafort’s Virginia home, in which they secured files stored on Manafort’s computer.

Prosecutors describe how Papadopoulos held himself out to be a conduit between the Trump campaign and high-level Russian officials, including Putin, from the start of his official involvement with the campaign.

Around that time, an unidentified London professor who had made contact with Papadopoulos claimed to have “dirt” on Clinton in the form of thousands of emails, according to the court filing. The professor was said to have substantial connections to Russian government officials.

That professor is Joseph Mifsud, the director of the London Academy of Diplomacy, the Washington Post reported. Mifsud didn’t respond to calls and texts from Bloomberg News requesting comment about his relationship with Papadopoulos. Mifsud is listed as a director of the London Centre of International Law Practice, where Papadopoulos worked from February to April 2016, according to his LinkedIn page. Calls to the center weren’t returned.

Mifsud’s biography, now deleted from the academy’s website, says he’s a member of the Valdai Group, which hosts annual meetings in Russia that have become a showcase for Putin’s policies.

In reality he attended the Valdai discussion group only in 2014 and didn’t return after accusations of plagiarism for an article he had published an article on the group’s website that contained plagiarized material, according to a person close to Valdai.

London Meeting

Papadopoulos met with the professor in London around March 21, 2016, prosecutors said. The professor brought with him a “female Russian national” introduced to Papadopoulos as a relative of Putin. There’s no evidence that the woman was indeed related to Putin.

Ten days later, according to the government’s statement of the offense, Papadopoulos attended a “national security meeting” that included Trump. When introduced at the meeting, Papadopoulos said he had connections he could use to arrange a meeting between Trump and Putin, it said.

That unnamed Russian national then began communicating with Papadopoulos. “As mentioned we are all very excited by the possibility of a good relationship with Mr. Trump,” she wrote in an April 2016 email disclosed by prosecutors. “The Russian Federation would love to welcome him once his candidature would be officially announced.”

Also around that time, prosecutors said, Papadopoulos emailed a high-ranking official of the Trump campaign “to discuss Russia’s interest in hosting Mr. Trump. Have been receiving a lot of calls over the last month about Putin wanting to host him and the team when the time is right.”

Days later, Papadopoulos thanked the professor for his “critical help” in arranging a meeting between campaign aides and the Russian government, saying, “It’s history making if it happens,” according to prosecutors.

Prosecutors say Papadopoulos deleted a Facebook account that included details about his meetings with the professor and another Russia-linked contact after his second interview with the FBI.

(An earlier version of this article corrected the type of filing in the Papadopoulos matter; it was a statement of facts.)